>Well. Isn't there login.conf? Yes, see manual, 'man login.conf' or online, https://www.dragonflybsd.org/cgi/web-man?command=login.conf§ion=ANY
..
SYNOPSIS
/etc/login.conf, ~/.login_conf
..
lang string Set $LANG environment
variable to the specified
value.
..
For LANG see 'man environ' or online,
https://www.dragonflybsd.org/cgi/web-man?command=environ§ion=ANY
-thomas
